Dual-Path Optical Recording Media and an Apparatus for Accessing Thereof

ABSTRACT

A dual-path optical recording medium and an apparatus for accessing such are disclosed. The dual-path optical recording medium includes a substrate, an intermediate recording layer, a holographic recording layer and a dichronic mirror layer. The intermediate recording layer is a rewritable data storage layer with a relatively low storage capacity. The holographic recording layer is a write-once data storage layer with a relatively high storage capacity. The dichronic mirror layer is located between the holographic recording layer and the intermediate recording layer. The apparatus for accessing the dual-path optical recording medium includes a first light module capable of generating a first laser light, and a second light module capable of generating a second laser light.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to Ser. No. ______, entitled“COMPUTER PROGRAM PRODUCT FOR CONTROLLING AN APPARATUS FOR ACCESSINGDUAL-PATH OPTICAL RECORDING MEDIA,” filed on even date (IBM docketnumber TU920060205US2), which is assigned to the assignee of the presentapplication.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to optical recording media in general, andmore particularly, to dual-path optical recording media. Still moreparticularly, the present invention relates to a method and apparatusfor accessing dual-path optical recording media.

2. Description of Related Art

In recent years, optical recording media with a large storage capacityhave been developed for storing various types of data, includingtextual, graphics and voice. An optical recording medium is typicallyprovided with a spiral or concentric track on one surface to allow laserbeams to be irradiated along the track when data recording or retrievalis being performed. A track is further divided into multiple sectorsthat become the minimum unit for recording information.

With the Digital Versatile Disk (DVD) technology, data can be recordedonto an optical recording medium via a light modulation recording methodfor modulating the intensity of a laser beam irradiated on a track ontowhich data are to be recorded. There are many types of optical recordingmedia, such as a phase change type optical disc, an organic pigment typeoptical disc, a magneto-optical disc, holographic media and the like.

SUMMARY OF THE INVENTION

The present disclosure provides a new type of optical recording mediaand an apparatus for accessing such optical recording media. Inaccordance with a preferred embodiment of the present invention, adual-path optical recording medium includes a substrate, an intermediaterecording layer, a holographic recording layer and a dichronic mirrorlayer. Having been stamped into one surface of the substrate to providelands and grooves, the intermediate recording layer is a rewritable datastorage layer with a relatively low storage capacity. The holographicrecording layer is preferably a write-once data storage layer with arelatively high storage capacity, but may be rewritable. The dichronicmirror layer is located between the holographic recording layer and theintermediate recording layer.

Data are written into the holographic recording layer in the form of ahologram. Data can be written to the holographic recording layer by afirst laser light having a wavelength of approximately 405 nm or 532 nm.The dichronic mirror layer is reflective to the first laser light. Datacan be written to the intermediate recording layer via a second laserlight having a wavelength of approximately 680 nm. The intermediaterecording layer includes a plurality of open hologram segments forstoring hologram segments. The intermediate recording layer includes anopen hologram segment directory for tracking hologram segments that havebeen opened. The intermediate recording layer includes a module forstoring policies that dictates the closing of any of the open hologramsegments.

A data recording system for accessing a dual-path optical recordingmedium includes a host, a first logical unit number (LUN) interface, asecond LUN interface, a first light module, and a second light module.The first light module capable of generating a first laser light iscoupled to the host via the first LUN interface. The second light modulecapable of generating a second laser light is coupled to the host viathe second LUN interface.

All features and advantages of the present invention will becomeapparent in the following detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as a preferred mode of use, furtherobjects, and advantages thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional diagram of a dual-path optical recordingmedium, in accordance to a preferred embodiment of the presentinvention;

FIG. 2 is a block diagram of a data recording system capable of readingand writing data to and from the optical recording medium from FIG. 1,in accordance with a preferred embodiment of the present invention; and

FIG. 3 is a detailed block diagram of various components within theoptical recording medium from FIG. 1, in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings, and specifically to FIG. 1, there isdepicted a cross-sectional diagram of a dual-path optical recordingmedium, in accordance with a preferred embodiment of the presentinvention. As shown, a dual-path optical recording medium 100 includes asubstrate 114, an intermediate recording layer 118, a gap layer 112, adichronic mirror layer 110, a gap layer 108, a holographic recordinglayer 104, and a transparent cover layer 102. Holographic recordinglayer 104 and intermediate recording layer 118 are two separaterecording layers of optical recording medium 100. Holographic recordinglayer 104 is preferably a write-once data storage layer having arelatively high storage capacity but it may be rewritable. In contrast,intermediate recording layer 118 is a rewritable data storage layerhaving a relatively low storage capacity. Being coated with aphase-change material that is commonly used in conventional DigitalVersatile Disks (DVDs), intermediate recording layer 118 is stamped intoone surface of substrate 114 to provide lands and grooves.

Data can be written into holographic recording layer 104 in the form ofa hologram, such as a hologram 106, by a first laser light 121 having awavelength of either 405 nm (blue) or 532 nm (green). Dichronic mirrorlayer 110 selectively reflects first laser light 121 such that firstlaser light 121 does not reach intermediate recording layer 118. For theholography write technology, as known in the art, a laser light beam issplit into two parts, a data beam and a reference beam. The data beam isencoded with data via a spatial light modulator, and the encoded databeam interferes with the reference beam to produce an interferencepattern that is stored on an optical recording medium as a hologram. Thehologram can subsequently be read by illuminating the hologram with thereference beam alone without need of the spatial light modulator. Forsimplicity, reference beam is shown in FIG. 1 as first laser light 121.

On the other hand, dichronic mirror layer 110 is selectively transparentto a second laser light 122 having a wavelength of 680 nm (which is thesame wavelength of a laser light for writing data to conventional DVDs).Thus, second laser light 122 can pass through dichronic mirror layer 110for writing data to (or reading data from) intermediate recording layer118.

In addition, intermediate recording layer 118 is reflective, and secondlaser light 122 can be reflected back to a holographic disk drive (notshown). Thus, second laser light 122 can also be employed as a servolaser by using the lands and grooves of intermediate recording layer 118to assist a servo of a holographic disk drive to track during thewriting and reading of a hologram, such as hologram 106, in holographicrecording layer 104. FIG. 1 is a cross-sectional illustration of opticalrecording media 100 that spins around a Z-axis, and the lands andgrooves of intermediate recording layer 118 about, or are concentricwith, the Z-axis.

With reference now to FIG. 2, there is illustrated a block diagram of adata recording system capable of reading and writing data to and fromoptical recording medium 100, in accordance with a preferred embodimentof the present invention. As shown, a data recording system 200 includesa host 201 having a host disk 202, a first logical unit number (LUN)interface 141, a second LUN interface 142, a first laser light module131 and a second laser light module 132. First laser module 131 andsecond laser module 132 are both located on a common sled (i.e., seekmechanism) 150. First laser light module 131 and second laser lightmodule 132 interface with host 201 via first LUN interface 141 andsecond LUN interface 142, respectively. First laser light module 131provides first laser light 121 to write (or read) holograms, such as ahologram 107, within holographic recording layer 104. Second laser lightmodule 132 provides second laser light 122 to write (or read) datawithin intermediate recording layer 118.

Data can be moved from intermediate recording layer 118 to holographicrecording layer 104, if necessary, based on frequent changes to the datanecessitating the random access. Since first laser module 131 and secondlaser module 132 communicate with each other via an interlayer bridge133, data can be removed from intermediate recording layer 118 and bewritten to holographic recording layer 104 without burdening host 201.

Referring now to FIG. 3, there is illustrated a detailed block diagramof various components within optical recording medium 100, in accordancewith a preferred embodiment of the present invention. As mentionedabove, optical recording medium 100 includes holographic recording layer104 and intermediate recording layer 118. Host 201 can write data tooptical recording medium 100 through a destage virtual track 205 usingdestage operations. A destage operation can be a SCSI write command, aSCSI write command across Fibre Channel, an iSCSI command, a GbENcommand, or any other similar command for writing data. Any datadestaged by host 201 can be optionally compressed before being writteninto one of open hologram segments 213 within intermediate recordinglayer 118. Compressed or uncompressed data for each new destageoperation is placed end-on-end with the data from prior destageoperations until one of open hologram segments 213 is completely filled.The size of one of open hologram segments 213 is preferably the same asthe size of a hologram stored within holographic recording layer 104, orthe same size as an integral number of hologram pages within holographicrecording layer 104.

Intermediate recording layer 118 can be used as a cache memory forholographic recording layer 104 to store data on a temporary basis. Butany data destined for final storage in holographic recording layer 104will eventually be migrated from intermediate recording layer 118 toholographic recording layer 104 according to a set of user-selectablepolicies 214.

The transfer of data from intermediate recording layer 118 toholographic recording layer 104 can be registered at host 201 (so host201 knows where to find the data) by updating a closed holographicsegment directory 203 within host disk 202 after the data have beentransferred.

An open hologram segment directory 212 is maintained in intermediaterecording layer 118 for each one of open holographic segments 213. Openhologram segment directory 212 records which tracks are being stored inopen hologram segments 213. After an open holographic 212 and openhologram segments 213 have been closed, both closed hologram segmentdirectory 222 and closed hologram segments 223 are then written toholographic recording layer 104, by passing them across interlayerbridge 133 that serves as a communication path between holographicrecording layer 104 and intermediate recording layer 118. Closedholographic directory 222 is also stored in closed holographic directory203 on host disk 202 so that host 201 knows how to find the respectiveone of closed holographic segments 223.

Any of open hologram segments 213 can be closed according to policies214. The hologram segment closing policies under policies 214 mayinclude parameters as follows:

I. A Maximum Time that a Hologram Segment can be Left Open

The hologram segment open time starts when the first data is written tointermediate recording layer 118. If the maximum time is not exceeded,but the open hologram segment 213 is full, the hologram segment can beclosed and be written to holographic recording layer 104 fromintermediate recording layer 118 via interlayer bridge 133. If themaximum time is exceeded and the open hologram segment 213 is not filledup to the segment capacity limit, the remaining space can be filled witha pad-pattern (i.e., a non-data pattern), and then the hologram segmentis closed and the data are written to holographic recording layer 104.Any hologram segment with a pad-pattern is marked “not full” in a closedhologram segment directory 203 within host disk 202 as well as closedhologram segment directory 222 within holographic recording layer 104.Otherwise, the non-data pattern used for padding may also include someerror correction code that are capable of providing additionalprotection to the data in hologram segments.

If new data arrives for a “not full” but closed hologram segment 223,that closed hologram segment 223 is retrieved from holographic recordinglayer 104 via interlayer bridge 133 to intermediate recording layer 118,to be re-opened. The new data is then appended to the now open hologramsegment 213, by overwriting the pad-pattern. The hologram segment issubsequently re-closed when the hologram segment is either completelyfilled or the maximum time is exceeded again.

This policy might be valuable to the credit card industry, where eachcredit card user has an open hologram segment for tracking his/herpurchases for a given credit card. The open hologram segment is createdat the beginning of each billing period or the first charge after thebeginning of the billing period, and then closed at the end of thatbilling period.

II. A Threshold Capacity for Closing a Hologram Segment

If the threshold capacity is exceeded, the hologram segment is closedand data are written to holographic layer 104. The threshold capacitymay be specified in holographic pages or in conventional storage units.The threshold of holographic pages is preferred when each holographicpage holds a predefined capacity and an integral number of pages isspecified as the threshold.

III. A Close Hologram Segment Command Issued by a User

If a hologram segment is not full when a close hologram segment commandis issued by a user, the remaining space is padded and new data causes aretrieval of the hologram segment and the new data are appended over thepad-pattern (same steps as policy I). A force closure of open hologramsegments 213 may also be invoked in response to a power outage orimpending disaster, such as a fire or hurricane.

IV. Only a Limited Number of Open Hologram Segments is Permitted

When too many open hologram segments 213 exist, the least recently used(LRU) hologram segments are closed first, as needed, to allow thecreation of new holographic segments. Alternatively, too many openhologram segments 213 can trigger an aggregation of manypartially-filled open hologram segments 213 into a few completely filledopen hologram segments 213, which then may be closed under Policy I.

V. When Data Compression is Allowed

A variant of this policy is that data in an open hologram segment 213 isnot compressed until that hologram segment reaches a capacity threshold,such as 90% filled. Once that threshold has been reached, data arecompressed on-demand in order to make room for additional data. Thispolicy is designed to mitigate the amount of padding used in policy I.

VI. Aggregating All Versions of a File in One Hologram Segment

The storage of multiple versions of a file allows a complete historicalrecord of changes made to the file. Thus, this policy is a logical formof holographic write-once-read-many (WORM), where multiple versions of afile are saved rather than overwritten. The advantage of this policy isthat all versions are stored in a common location so that a user doesnot have to engage in multiple accesses of a holographic medium toretrieve different versions. This policy may be valuable for theretention of financial and legal records.

VII. Mirroring Between Hologram Segments

When a file can be mirrored between two hologram segments—for redundantarray of independent disk (RAID)-1 emulation, if one hologram segmentcannot be read from a holographic medium, the same file can be accessedvia the mirrored hologram segment.

VIII. Striping Data Across Multiple Hologram Segments

Information in three or more hologram segments may be spread into RAIDstripes with parity stored in one hologram segment for a RAID-3 orRAID-4 emulation, or with parity spread across several hologram segmentsfor a RAID-5 emulation. The closed hologram directory 222 and closedhologram segments 223 can be written into holographic recording layer104 as a single hologram or a single group of holograms, and the newlyclosed hologram directory 222 is copied to host 201 in order to updateoverall hologram segment directory 203 stored within host disk 202. Atthis point, intermediate recording layer 118 ceases to retain anyinformation about the hologram segment that has just been closed inorder to make room for new open segments 213 and open segmentdirectories 212.

More than one policy within policies 214 may be activatedsimultaneously. Although policies 214 can be executed within host 201,it is preferable for policies 214 to be executed within a drive 199 sothat host 201 is not burdened by policy executions.

Data can be written by host 201 separately to intermediate recordinglayer 118 using second LUN interface 142 (from FIG. 2) or to holographicrecording layer 104 using first LUN interface 141 (from FIG. 2) viadestage virtual track 205. For example, fossilized (such as quiescent ordormant) data may be written directly to holographic recording layer104, bypassing intermediate recording layer 118. Data which is activeand may be frequently changed may be first written to intermediaterecording layer 118, which then forms a cache for holographic recordinglayer 104. Once an activity has deemed to be quiescent, the data may bemigrated from intermediate recording layer 118 to holographic recordinglayer 104, via interlayer bridge 133.

Alternately, if there is a problem writing closed hologram segments 223from host 201 directly to holographic layer 104, that data may betemporarily written as open hologram segments 213 from LUN interface 141across interlayer bridge 133 to intermediate recording layer 118. Later,once the problem is resolved, the data may be migrated to the originaldestination of holographic recording layer 104, as closed hologramsegments 223, again by use of interlayer bridge 133.

As has been described, the present invention provides a dual-pathoptical recording medium, and an apparatus and methods for accessingsuch.

While an illustrative embodiment of the present invention has beendescribed in the context of a fully functional computer system withinstalled software, those skilled in the art will appreciate that thesoftware aspects of an illustrative embodiment of the present inventionare capable of being distributed as a computer program product in avariety of forms, and that an illustrative embodiment of the presentinvention applies equally regardless of the particular type of signalbearing media used to actually carry out the distribution. Examples ofsignal bearing media include recordable type media such as floppy disks,hard drives, compact discs, integrated circuit device and transmissiontype media such as digital and analog communication links.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

1. A dual-path optical recording medium comprising: a substrate; anintermediate recording layer stamped into one surface of said substrateto provide lands and grooves, wherein said intermediate recording layeris a rewritable data storage layer having a relatively low storagecapacity; a holographic recording layer is a write-once data storagelayer having a relatively high storage capacity; and a dichronic mirrorlayer located between said holographic recording layer and saidintermediate recording layer.
 2. The recording medium of claim 1,wherein data are written into said holographic recording layer in theform of a hologram.
 3. The recording medium of claim 1, wherein data canbe written to said holographic recording layer by a first laser lighthaving a wavelength of approximately 405 nm or 532 nm.
 4. The recordingmedium of claim 3, wherein said dichronic mirror layer is reflective tosaid first laser light.
 5. The recording medium of claim 1, wherein datacan be written to said intermediate recording layer via a second laserlight having a wavelength of approximately 680 nm.
 6. The recordingmedium of claim 1, wherein said intermediate recording layer includes aplurality of open hologram segments for storing hologram segments. 7.The recording medium of claim 6, wherein said intermediate recordinglayer includes an open hologram segment directory for tracking hologramsegments that have been opened.
 8. The recording medium of claim 7,wherein said intermediate recording layer includes a module for storingpolicies that govern the closing of any of said open hologram segments.9. The recording medium of claim 6, wherein said holographic recordinglayer includes a plurality of closed hologram segments for storing saidopen hologram segments after they have been closed.
 10. The recordingmedium of claim 7, wherein said holographic recording layer includes aclosed hologram segment directory for storing said open hologram segmentdirectory after it has been closed.
 11. An apparatus for accessing adual-path optical recording medium, said apparatus comprising: a firstlogical unit number (LUN) interface and a second LUN interface; a firstlight module, coupled to said first LUN interface, for generating afirst laser light; and a second light module, coupled to said second LUNinterface, for generating a second laser light.
 12. The apparatus ofclaim 11, wherein said first laser light has a wavelength ofapproximately 405 nm or 532 nm.
 13. The apparatus of claim 11, whereinsaid second laser light has a wavelength of approximately 680 nm. 14.The apparatus of claim 11, wherein said first and second light modulesare located on a common sled.
 15. The apparatus of claim 11, whereinsaid apparatus further includes an interlayer bridge connected betweensaid first and second light modules for allowing communications betweensaid first and second laser modules.
 16. The apparatus of claim 11,wherein said dual-path optical recording medium includes a substrate; anintermediate recording layer located on one surface of said substrate tobe accessed by said second laser light; and a holographic recordinglayer to be accessed by said first laser light.
 17. The apparatus ofclaim 16, wherein said dual-path optical recording medium furtherincludes a dichronic mirror layer located between said holographicrecording layer and said intermediate recording layer.
 18. The apparatusof claim 16, wherein said intermediate recording layer is a rewritabledata storage layer having a relatively low storage capacity.
 19. Theapparatus of claim 16, wherein said holographic recording layer is awrite-once data storage layer having a relatively high storage capacity.20. The apparatus of claim 16, wherein said interlayer bridge allowsdata to be transferred directly from one recording layer to anotherrecording layer of said dual-path optical recording medium without goingthrough a host computer.
 21. A data recording system comprising: a hostcomputer; and a drive for accessing a dual-path optical recordingmedium, wherein said drive includes a first logical unit number (LUN)interface and a second LUN interface; a first light module coupled tosaid host via said first LUN interface, wherein said first light modulegenerates a first laser light; and a second light module coupled to saidhost via said second LUN interface, wherein said second light modulegenerates a second laser light.
 22. The data recording system of claim21, wherein said first laser light has a wavelength of approximately 405nm or 532 nm.
 23. The data recording system of claim 21, wherein saidsecond laser light has a wavelength of approximately 680 nm.
 24. Thedata recording system of claim 21, wherein said first and second lightmodules are located on a common sled.
 25. The data recording system ofclaim 21, wherein said drive further includes an interlayer bridgelocated between said first and second light modules for allowingcommunications between said first and second laser modules.
 26. The datarecording system of claim 21, wherein said dual-path optical recordingmedium includes a substrate; an intermediate recording layer located onone surface of said substrate to be accessed by said second laser light;and a holographic recording layer to be accessed by said first laserlight.
 27. The data recording system of claim 26, wherein said dual-pathoptical recording medium further includes a dichronic mirror layerlocated between said holographic recording layer and said intermediaterecording layer.
 28. The data recording system of claim 26, wherein saidintermediate recording layer is a rewritable data storage layer having arelatively low storage capacity, and said holographic recording layer isa write-once data storage layer having a relatively high storagecapacity.
 29. The data recording system of claim 26, wherein saidinterlayer bridge allows data to be transferred directly between saidholographic recording layer and said intermediate recording layerwithout going through said host computer.